Field of the Invention
The present invention relates to correction of aberration distortions, in particular by image processing, in an image formation optical system, such as a digital camera provided with the electronic imaging optical system.
Background of the Invention
In the imaging system of a digital camera image formation is conventionally carried out by an imaging lens that projects an object image onto an image sensor. The image sensor has a plurality of optoelectric transducers arranged in a matrix form that provide for a photoelectric conversion of the object image projected by the lens. An image processing device using an image processing method then generates an output image using the picture signal provided by the image sensor.
In current digital camera's, the pixel positions of the output image, match with those of the picture obtained from the image sensor (also denoted as input image). Each pixel signal sampled from the input image is converted into a pixel signal for the output image.
A lens of an optical system generally causes a geometric distortion by aberration in a picture obtained therewith. This deteriorates the accuracy and quality of the picture. Various measures are taken to reduce this aberration.
For example, it is known to reduce the distortion by aberration of a lens by combining two or more lenses. However, this increases the costs and negatively influences productivity.
Image signal processing methods are known to control aberration distortion in a digitized picture obtained by image formation using a lens.
For example, the pixel coordinate of a reference picture not having a aberration distortion are compared with the coordinates in the picture obtained from the image projected by the lens on the image sensor. A memory stores for each sampling position in the output image the corresponding coordinates in the reference image. Then, an arbitrary picture is compensated for aberration distortion, by reading the correct sampling coordinates for each sampling position from the memory.
For every pixel of an output image, the sampling position to an input image is converted using a high order polynomial. By sampling the input image in the converted sampling position an aberration distortion should be compensated. Such a method of controlling a aberration distortion is known for example from patent documents 1 and 2.
Patent documents 1: JP 2000-324339 A
Patent documents 2: JP 10-262176 A